My wife is LDS. I spend a lot of time with members of her Ward and have even attended her Sacrament Meetings, even though I and our kids are Catholic.
Missions last 2 years. They aren't mandatory but encouraged. Usually it is a family encouragement, like everyone in the family has done it, so now it's your turn. Both men and women go on missions. You get assigned a certain geographic region. Say you are on a mission in Boise. Well, you are probably assigned Idaho and part of Washington. Every few months you are likely to get transferred to another area (or Stake) in the region, but you stay in that region. You also get partnered with someone and have to be together at all times. You can't have a girlfriend, or boyfriend. You can't leave your assigned area without permission from the Mission President. You can't call home unless it's Mother's Day or Christmas. You have one day a week to check email. You can get letters through snail mail though. You basically make appointments to speak to people about becoming LDS by giving lessons. You also do physical work for people who need their yards cleared or things like that.
This is not everything and might not be totally accurate. I'm not LDS, like I said. But I've had extensive talks and have spent extensive time with people who are LDS. They made sure I was pretty clear on everything when my wife was becoming LDS. They don't want problems to occur in the marriage due to the religion. So this is probably pretty close to spot on.
I don't know if exceptions are made for people. I don't think so. When someone LDS goes to the Temple, they put on a white jumpsuit because everyone is equal in front of God. So I don't know if they would make an exception because someone is good at football. But if he does go on a mission, it is likely he will miss 2 years and come back a better person for it.
